The get settings API can be used to get settings for more than one index
with a single call. General usage of the API follows the
following syntax: host:port/{index}/_settings where
{index} can stand for comma-separated list of index names and aliases. To
get settings for all indices you can use _all for {index}.
Wildcard expressions are also supported. The following are some examples:

GET /twitter,kimchy/_settings
GET /_all/_settings
GET /log_2013_*/_settings